1. Field of the Invention
The present invention relates to an optical pickup device for recording and/or reproducing information to and/or from an optical recording medium, and an optical recording medium driving device.
2. Description of the Background Art
A conventional optical pickup device is constructed in such a manner that a P-polarized laser beam is outputted from a semiconductor laser device, and the outputted laser beam is incident onto a photodetector and received by the photodetector after part of the outputted laser beam is reflected on a beam splitter through a collimator lens. The photodetector converts the received laser beam into an electric signal. The electric signal converted by the photodetector is used for controlling the power of the laser beam. Primary part of the laser beam is incident onto an objective lens through the beam splitter, and is condensed on a surface of an optical disc. The laser beam reflected on the optical disc is incident onto the beam splitter again through the objective lens. The laser beam incident onto the beam splitter is reflected thereon and incident onto a servo signal detector and an information signal detector to be received by the servo signal detector and the information signal detector. The servo signal detector converts the received laser beam into an electric signal. The electric signal converted by the servo signal detector is used as a control signal for a servo system. The information signal detector converts the received laser beam into an electric signal. The electric signal converted by the information signal detector is used as an information signal (see e.g. Japanese Unexamined Patent Publication No. Sho 62-140253).
In the conventional optical pickup device, since the P-polarized laser beam is incident onto the beam splitter, the amount of light directed to the objective lens may be reduced. In view of this, in the conventional optical pickup device, a reflectance of the beam splitter is lowered to increase the amount of light directed to the objective lens. This may increase a variation in light amount detected by the photodetector resulting from a variation in recording layer thickness.
In the case where the reflectance of the beam splitter is lowered, a change in light amount detected by the photodetector relative to the wavelength may be increased due to wavelength dependence of the reflectance, and the light amount detected by the photodetector may be changed due to a wavelength change of a laser beam resulting from a temperature change. This may make it difficult to accurately control the power of the laser beam.